package/gnupg2: add optional support for libusb-compat

When libusb-compat was compiled before, gnupg2 will use it as optional
dependency:

$ output/host/usr/bin/x86_64-linux-readelf -a output/target/usr/libexec/scdaemon | grep NEEDED
[...]
 0x0000000000000001 (NEEDED)             Shared library: [libusb-0.1.so.4]
[...]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/gnupg2/gnupg2.mk

@@ -38,6 +38,13 @@ else
 GNUPG2_CONF_OPTS += --disable-bzip2
 endif
 
+ifeq ($(BR2_PACKAGE_LIBUSB_COMPAT),y)
+GNUPG2_CONF_OPTS += --enable-ccid-driver
+GNUPG2_DEPENDENCIES += libusb-compat
+else
+GNUPG2_CONF_OPTS += --disable-ccid-driver
+endif
+
 ifeq ($(BR2_PACKAGE_READLINE),y)
 GNUPG2_CONF_OPTS += --with-readline=$(STAGING_DIR)
 GNUPG2_DEPENDENCIES += readline